The Metropolitan Transportation Authority (MTA), which runs Metro-North, issued a statement today explaining that technicians took one of two main power supply units out of service for replacement, without realizing a wire was disconnected on the second unit.

The power system was "destabilized" at 7:45 p.m. Without reliable power for the signal system, the MTA halted more than 50 trains for safety reasons. The trains themselves had power, light and heat, and no passengers were endangered, the MTA says.

It took an hour and a half to connect a backup supply, and trains got moving again by 9:30 p.m. Full control was re-established an hour later. Service returned to normal on Friday morning.

"Metro-North customers deserve better, and I extend my sincere apology to all of them," MTA Chairman and CEO Thomas F. Prendergast said in the statement.

"I have directed Metro-North to bring in an independent consultant to examine how and why these mistakes were made, and to recommend any necessary changes to operating procedures to ensure nothing like this ever happens again."